LOCAL HOLE DISTRIBUTION IN THE CUO2 PLANE OF HIGH-T-C CU-OXIDES STUDIED BY CU AND OXYGEN NQR NMR/

The hole numbers at Cu and oxygen sites in the CuO2 plane in a wide va riety of high-T-c materials have been extracted from the measured nucl ear quadrupole frequency, nu(Q). The hole number in the Cu-3d(x2-y2) o rbit, n(x2-y2), is found to be more than 0.85 in La2-xSrxCuO4 (x = 0.0 75-0.24), while decreases to 0.74 in Tl2Ba2Ca2Cu3O10. Thus estimated n (x2-y2) is supported by the result that the orbital Knight shift along the c-axis, K-orb(c) increases in proportion to n(x2-y2), in contrast to the decrease of n(x2-y2), the hole number in the O-2p(o) orbit, n( po), increases in going from the La- to the Tl-systems. It has been fo und that T-c is determined by two parameters about holes, i.e., n(x2-y 2) + 2n(po) and n(x2-y2)/2n(po). The former tells the microscopic ''do ping level'' of the CuO2 plane, while a smaller n(x2-y2)/2n(po) result s in a weaker antiferromagnetic spin fluctuations of low energy. It ha s been found that not only a proper n(x2-y2) + 2n(po) but also a suffi ciently small n(x2-y2)/2n(po)( similar or equal to 1) are needed to ob tain a high value of T-c.